The present invention relates to an improvement in a packaging machine using a heat-shrinkable film and provided with a shrinkage tunnel.
In the known art packaging machines using heat-shrinkable films are known and they comprise a frame for sealing of the film surrounding the product to be packaged and a shrinkage tunnel providing circulation of hot air in a continuous cycle.
A conveyor belt carries out passage through the tunnel of the products wrapped in the film already sealed by means of the frame. The film grazed by the hot air circulating within the tunnel shrinks on the product thereby packaging it.
In these shrinkage tunnels, air circulation through the electrical heating elements takes place in a continuous manner and temperature adjustment is carried out by a probe measuring the air temperature and sending a signal to an appropriate thermoregulator adjusting the heating power of the electrical heating elements.
This way of operating involves a high energy consumption and a high thermal pollution in the work environment due to continuous emission of hot air. On the other hand, if air heating is reduced, film shrinkage becomes unsatisfactory. It is a general aim of the present invention to obviate the above mentioned drawbacks by providing a packaging machine of the above type, which allows high energy saving while keeping a satisfactory heat-shrinkage of the film.
In view of the above aim, in accordance with the invention a packaging machine using a heat-shrinkable film has been devised which comprises a frame for peripheral sealing of a film segment and a tunnel disposed alongside the frame in which means is arranged for circulation of the air heated by electrical heating elements for shrinkage of the sealed film which is introduced into the tunnel, characterised in that it comprises means for detecting a condition associable with the presence in the machine of a product wrapped in a film to be shrunk, the detecting means, upon detection of said condition, producing a signal for temporary actuation of the hot-air circulation means.